1. Field of the Invention
The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery which has excellent life span property and penetration safety.
2. Description of the Related Art
With rapid progress of electronic, telecommunication and computer industries, portable electronic communication devices such as a camcorder, mobile phone, notebook PC, etc. have been remarkably developed. Accordingly, the demand for a lithium secondary battery as a power source capable of driving the above device is also increased day by day. In particular, with regard to applications of eco-friendly power sources such as an electric car, uninterruptible power supply, electromotive tool and satellite, research and development have been actively proceeded in domestic field and other countries such as Japan, Europe, United States, etc.
Among currently used secondary batteries, the lithium secondary battery developed since early 1990's includes an anode electrode made of a carbon material capable of absorbing and desorbing lithium ions, a cathode electrode made of lithium-containing oxide, and a non-aqueous electrolyte containing lithium salt dissolved in a mixed organic solvent in a suitable amount.
In this regard, as the application of the lithium secondary battery is more enlarged, a case that the lithium secondary battery should be used even under more severe environments is increased.
However, lithium transition metal oxide or composite oxide used as a cathode active material of the lithium secondary battery entails a problem that a metal component is desorbed from the cathode electrode during storage at a high temperature under fully charged condition, hence being in thermally unstable state. In addition, when a forced internal short circuit occurs due to an external impact, a heating value inside the battery is rapidly increased, thereby causing ignition.
In order to solve the above problems, Korean Patent Laid-Open Publication No. 2006-0134631 discloses a cathode active material having a core-shell structure in which a core part and a shell part are made of lithium transition metal oxides different from each other, however, still has lack of improvement in life-span property and safety of the battery.